1. Technical Field
The present invention relates to a driver circuit and a test apparatus. More particularly, the present invention relates to a driver circuit that outputs an output signal according to an input signal and a test apparatus that tests a device under test.
2. Related Art
A test apparatus that tests a device under test, such as a semiconductor device, is provided with a driver circuit that supplies a test signal to the device under test. Furthermore, the test apparatus is provided with a plurality of types of driver circuits and the type of driver circuit is selected according to the test signal to be supplied to the device under test.
In a case where a large amplitude test signal is supplied, the test apparatus selects, for example, a large amplitude driver circuit that includes a power amplifier that amplifies the power of the test signal. Furthermore, in a case where a high speed and high precision test signal is provided, the test apparatus selects, for example, a high speed driver circuit that includes a differential amplifier that differentially amplifies the test signal.
In a case where the large amplitude test signal and the high speed and high precision test signal can both be output from one output end, the test apparatus must be provided with a single driver circuit that includes the functions of both the large amplitude driver circuit and the high speed driver circuit. However, it is difficult to realize a single driver circuit that includes the functions of both the large amplitude driver circuit and the high speed driver circuit.
For example, realizing the large amplitude and high speed driver circuit by enlarging the amplitude of the output signal of the high speed driver circuit can be considered. To enlarge the amplitude of the output signal of the high speed driver circuit, the differential amplifier should be configured to cause a large current to flow to the output resistor. Here, in a case where the differential amplifier causes the large current to flow to the output resistor, a transistor with a large voltage endurance for controlling a bias and connected serially to the output resistor must be provided.
However, the transistor having the large voltage endurance has a large collector capacity, which slows response speed. Therefore, when the amplitude of the output signal of the high speed driver circuit is enlarged, the response speed is undesirably slowed. Accordingly, it is difficult to realize the large amplitude and high speed driver circuit by enlarging the amplitude of the output signal of the high speed driver circuit.
On the other hand, realizing the large amplitude and high speed driver circuit by causing the large amplitude driver circuit to operate at a high speed can be considered. To cause the large amplitude driver circuit to operate at a high speed, the differential amplifier should be disposed in front of the power amplifier. However, in a case where the differential amplifier is disposed in front of the large amplitude driver circuit, the amplitude of the output signal of the differential amplifier must be enlarged. When the differential amplifier is caused to operate with a large amplitude, the response speed of the output signal is slowed, as described above. Accordingly, it is difficult to realize the large amplitude and high speed driver circuit by causing the large amplitude driver circuit to operate at a high speed.
Furthermore, there are cases where the large amplitude driver circuit is provided with a class-AB power amplifier as the power amplifier. In such a case, the output impedance of the large amplitude driver circuit is undesirably changed according to a load current. Accordingly, it is difficult for the large amplitude driver circuit to supply an accurate output signal to the device under test.